Field of the Invention
The present invention relates to a cooling system for heat insulating engines made of ceramic materials.
Description of the Prior Art
In general reciprocal engines, the exterior of the reciprocating piston is cooled either by water or air to enable continued smooth reciprocating motion of the piston. When a combustion chamber defined by a cylinder liner, a cylinder head and a piston head is heat-insulated, the combustion energy of the fuel is contained in the exhaust gas or converted into work. In conventional cooling systems of the engines, cooling chambers or water jackets 88 are formed, as shown in FIG. 8, not only in the cylinder head and in the upper part of the cylinder liner but also in a cylinder block 87 at the lower part of the cylinder liner 89 in which the piston reciprocates. These water jackets occupy a large space in the engine and their complicated shapes make the casting and machining operations difficult, which in turn makes it impossible to reduce the weight and cost of the engines. Furthermore, since the amount of cooling water is large, it takes time for the cooling water to become warm, requiring a longer idling of the engine.
A conventional cooling system for the heat insulating engine is disclosed, for example, in the Japanese Utility Model Laid-Open No. 15921/1985. This cooling system for the heat insulating engine will be explained by referring to FIG. 9. The heat insulating engine cooling system consists of: cooling chambers 92, 93 formed in two vertically separated layers in a cylinder block 91 around the lower part of the cylinder liner; temperature sensors 94, 95 installed in the cooling chambers 92, 93 to detect the temperatures of coolant; and a controller 104 for sending to a coolant driving means 105 a coolant flow velocity control signal corresponding to the detected temperature signals from the temperature sensors 94, 95. The controller 104 controls the flow speed of the coolant in the cooling chambers 92, 93. Inside a cylinder head 103--formed integral with an extension 97 surrounding the upper part of the cylinder liner--is fitted a liner head 100 which consists of a cylinder head internal wall portion 99 and an upper part 96 of the cylinder liner, formed in one piece. Cooling chambers 102 are formed near the cylinder head 103. The cylinder block 91 and the cylinder head 103 are made of casting. The liner head 100 is made of a silicon nitride (Si.sub.3 N.sub.4) or partially stabilized zirconia (PSZ). The cylinder liner 98 is formed of PSZ and securely installed into the cylinder block 91 through shrink fit or press fit. The piston head 101 is made of silicon nitride. In the figure, the reference symbol A and B represent the directions of coolant flow.
A cylinder head cooling system for the heat insulating engine disclosed in the Japanese Utility Model Laid-Open No. 14715/1986 has a combustion chamber which has a heat insulating structure formed of a ceramic material. In this heat insulating structure, the coolant flow to the water jacket formed in the cylinder head around the exhaust valve is controlled according to a specified engine characteristic value to maintain the performance of the exhaust valve. That is, the cooling system has a coolant control means which, according to the exhaust gas temperature, revolution speed, and boosting pressure of the engine, supplies the coolant into the water jacket that is formed in the metal cylinder head body assembled on the head plate or at least around the exhaust valve.
The Japanese Patent Laid-Open No. 191414/1982 discloses a cooling system for reciprocating engines in which cooling chambers are formed in the cylinder head and in the cylinder body around the upper and lower part of the cylinder liner. The cooling system has an engine water pump controller which consists of: a driving device for driving the water pump independently of the engine revolution speed; a temperature sensor for detecting the engine temperature; and a controller which controls the water pump driving device in such a way as to increase the water pump revolution speed when the engine temperature from the temperature sensor is higher than the stabilized temperature by more than a setting value.
A cylinder block for the internal combustion engine disclosed in the Japanese Patent Laid-Open No. 13957/1985 is similar to the one 87 shown in FIG. 8. The cylinder block has water jackets formed around a plurality of cylinders. Side walls arranged outside the cylinders are formed recessed inwardly between the cylinders. The notable structure of this cylinder block is that first reinforcement ribs and second reinforcement ribs are formed on the cylinder block. The first reinforcement ribs are formed projecting externally from the side walls between the cylinders near the lower deck to connect the adjacent side walls. The second reinforcement ribs are formed projecting externally from the side walls to connect the upper and lower parts of the cylinder block through the first reinforcement ribs. This type of cylinder block has the water jackets in which cooling water is circulated, and these ribs are formed on the cylinder block around the water jacket. The ribs are intended to increase the rigidity and strength of the cylinder block, thereby preventing deformation and reducing vibration. However, no measures have yet been taken as to the cylinder liner which is a source of noise.